The present invention relates to a semiconductor device and a method of manufacturing the same and, more particularly, to technology for preventing corrosion of a metal wire made of an aluminum alloy containing copper, which is formed on a semiconductor substrate.
In general, corrosion of metal is greatly affected by a state on the surface thereof. For example, aluminum used in a metal wire formed on a semiconductor substrate exhibits improved resistance to corrosion with an extremely thin native oxide film densely formed on the surface thereof.
However, when a metal film made of aluminum formed on the semiconductor substrate is subjected to dry etching using etching gas containing chlorine gas, a residue of chlorine ions contained in the etching gas may react disadvantageously with moisture contained in an atmosphere to form a hydrochloric acid, which causes corrosion of the native oxide film on aluminum.
To remove the residual chlorine ions after dry etching using the etching gas containing chlorine gas, there has been proposed a method of substituting fluorine ions for the chlorine ions by plasma processing using CF.sub.4, thereby forming an organic film for protecting the metal wire on the surface of aluminum (Japanese Laid-Open Patent Publication HEI 2-26029). To prevent the reaction between the chlorine ions and the moisture contained in the atmosphere, there have been proposed a method of oxidizing the surface of aluminum with an oxidizing agent so as to passivate aluminum, i.e., to form an oxide film on the surface thereof (Japanese Laid-Open Patent Publication SHO 63-293861) and a method of performing etching under vacuum so as to prevent the metal wire from being exposed to the atmosphere after etching (Japanese Laid-Open Patent Publication SHO 60-5928).
For verification, the present inventors have made various examinations of the foregoing methods of preventing corrosion of the metal wire to find that, though the foregoing methods are effective with respect to a metal wire made of aluminum, they are not perfectly effective with respect to a metal wire made of an aluminum alloy containing copper, which has been added to improve resistance to electromigration.
This is because a potential difference produced between aluminum and about several percent of copper added thereto forms a local cell, which may cause corrosion on the surface of the metal wire merely by immersing the metal wire in pure water during a cleaning process or the like. However, no prevention measure has been taken previously against the corrosion resulting from the local cell effect caused by the potential difference between aluminum and copper.